//for...in  vs for...of
//for..of遍历所有迭代器，出现的内容
//for...in 遍历万物，出现的是下标

let arr = [1,2,3]
let str = 'hello'

let obj = {
    name: 'John',
    age: 30
}
for (let i of arr) {
    console.log(i);
    
}

for (let  i in arr){
    console.log(i); // 下标
    
}